Asymmetrical siloxy compounds

ABSTRACT

The present invention relates to asymmetrical siloxy compounds of the formula ##STR1## wherein R 1 , R 2  and R 3  are independently selected from the group consisting of alkoxy radicals having from 1 to 8 carbon atoms; R 4  is selected from the group consisting of alkylene groups having from 1 to 15 carbon atoms and arylene and alkyl-substituted arylene groups having from 6 to 10 carbon atoms; n is an integer of from 2 to 8 and X is selected from the group consisting of ##STR2## and R 5  is selected from the group consisting of alkyl groups having from 1 to 15 carbon atoms, aryl and alkyl substituted aryl groups having 6 to 10 carbon atoms.

FIELD OF THE INVENTION

The present invention relates to a compound which is useful insilica-filled rubber compositions and the processing of a sulfur curablerubber composition containing silica.

BACKGROUND OF THE INVENTION

Sulfur containing organosilicon compounds are useful as reactivecoupling agents between rubber and silica fillers providing for improvedphysical properties. They are also useful as adhesion primers for glass,metals and other substrates.

U.S. Pat. Nos. 3,842,111, 3,873,489 and 3,978,103 disclose thepreparation of various sulfur containing organosilicon compounds. Theseorganosilicon compounds are prepared by reacting

(a) 2 moles of a compound of the formula

    Z-Alk-hal

where hal is a chlorine, bromine or iodine; Z is ##STR3## where R¹ is analkyl of 1 to 4 carbon atoms or phenyl and R₂ is alkoxy of 1 to 8 carbonatoms; or cycloalkoxy of 5 to 8 carbon atoms; or alkylmercapto with 1 to8 carbon atoms; Alk is a divalent aliphatic hydrocarbon or unsaturatedhydrocarbon or a cyclic hydrocarbon containing 1 to 18 carbon atoms;with

(b) 1 mole of a compound of the formula

    Me.sub.2 S.sub.n

where Me is ammonium or a metal atom and n is a whole number from 2 to6.

Japanese Patent Application No. 124400-1984 and U.S. Pat. No. 4,820,751each disclose a rubber composition containing a silicate-based fillerand a compound containing siloxy groups and a benzothiazole group. Oneexample of such compound istrimethyoxysilylpropyl-mercaptobenzothiazoletetrasulfide.

SUMMARY OF THE INVENTION

The present invention relates to asymmetrical siloxy compounds of theformula: ##STR4## wherein R¹, R² and R³ are independently selected fromthe group consisting of alkoxy radicals having from 1 to 8 carbon atoms;R⁴ is selected from the group consisting of alkylene groups having from1 to 15 carbon atoms and arylene and alkyl-substituted arylene groupshaving from 6 to 10 carbon atoms; n is an integer of from 2 to 8 and Xis selected from the group consisting of ##STR5## and R⁵ is selectedfrom the group consisting of alkyl groups having from 1 to 15 carbonatoms, aryl and alkyl substituted aryl groups having 6 to 20 carbonatoms.

DETAILED DESCRIPTION OF THE INVENTION

There is also disclosed a method for processing a silica-filled rubbercomposition which comprises

(i) 100 parts by weight of at least one elastomer containing olefinicunsaturation selected from conjugated diene homopolymers and copolymersand from copolymers of at least one conjugated diene and aromatic vinylcompound;

(ii) 10 to 250 phr of particulate precipitated silica;

(iii) 0 to 150 phr of carbon black; and

(iv) 0.05 to 10 phr of a compound of the formula ##STR6## wherein R¹, R²and R³ are independently selected from the group consisting of alkoxyradicals having from 1 to 8 carbon atoms; R⁴ is selected from the groupconsisting of alkylene groups having from 1 to 15 carbon atoms andarylene and alkyl-substituted arylene groups having from 6 to 10 carbonatoms; n is an integer of from 2 to 8 and X is selected from the groupconsisting of ##STR7## and R⁵ is selected from the group consisting ofalkyl groups having from 1 to 15 carbon atoms, aryl and alkylsubstituted aryl groups having 6 to 20 carbon atoms.

There is also disclosed a silica-filled rubber composition comprising anelastomer containing olefinic unsaturation, silica and a compound of theformula ##STR8## wherein R¹, R² and R³ are independently selected fromthe group consisting of alkoxy radicals having from 1 to 8 carbon atoms;R⁴ is selected from the group consisting of alkylene groups having from1 to 15 carbon atoms and arylene and alkyl-substituted arylene groupshaving from 6 to 10 carbon atoms; n is an integer of from 2 to 8 and Xis selected from the group consisting of ##STR9## and R⁵ is selectedfrom the group consisting of alkyl groups having from 1 to 15 carbonatoms, aryl and alkyl substituted aryl groups having 6 to 20 carbonatoms.

The present invention may be used to process sulfur vulcanizable rubbersor elastomers containing olefinic unsaturation. The phrase "rubber orelastomer containing olefinic unsaturation" is intended to include bothnatural rubber and its various raw and reclaim forms as well as varioussynthetic rubbers. In the description of this invention, the terms"rubber" and "elastomer" may be used interchangeably, unless otherwiseprescribed. The terms "rubber composition", "compounded rubber" and"rubber compound" are used interchangeably to refer to rubber which hasbeen blended or mixed with various ingredients and materials and suchterms are well known to those having skill in the rubber mixing orrubber compounding art. Representative synthetic polymers are thehomopolymerization products of butadiene and its homologues andderivatives, for example, methylbutadiene, dimethylbutadiene andpentadiene as well as copolymers such as those formed from butadiene orits homologues or derivatives with other unsaturated monomers. Among thelatter are acetylenes, for example, vinyl acetylene; olefins, forexample, isobutylene, which copolymerizes with isoprene to form butylrubber; vinyl compounds, for example, acrylic acid, acrylonitrile (whichpolymerize with butadiene to form NBR), methacrylic acid and styrene,the latter compound polymerizing with butadiene to form SBR, as well asvinyl esters and various unsaturated aldehydes, ketones and ethers,e.g., acrolein, methyl isopropenyl ketone and vinylethyl ether. Specificexamples of synthetic rubbers include neoprene (polychloroprene),polybutadiene (including cis-1,4-polybutadiene), polyisoprene (includingcis-1,4-polyisoprene), butyl rubber, styrene/isoprene/butadiene rubber,copolymers of 1,3-butadiene or isoprene with monomers such as styrene,acrylonitrile and methyl methacrylate, as well as ethylene/propyleneterpolymers, also known as ethylene/propylene/diene monomer (EPDM), andin particular, ethylene/propylene/dicyclopentadiene terpolymers. Thepreferred rubber or elastomers are polybutadiene and SBR.

In one aspect the rubber is preferably of at least two of diene basedrubbers. For example, a combination of two or more rubbers is preferredsuch as cis 1,4-polyisoprene rubber (natural or synthetic, althoughnatural is preferred), 3,4-polyisoprene rubber,styrene/isoprene/butadiene rubber, emulsion and solution polymerizationderived styrene/butadiene rubbers, cis 1,4-polybutadiene rubbers andemulsion polymerization prepared butadiene/acrylonitrile copolymers.

In one aspect of this invention, an emulsion polymerization derivedstyrene/butadiene (E-SBR) might be used having a relatively conventionalstyrene content of about 20 to about 28 percent bound styrene or, forsome applications, an E-SBR having a medium to relatively high boundstyrene content, namely, a bound styrene content of about 30 to about 45percent.

The relatively high styrene content of about 30 to about 45 for theE-SBR can be considered beneficial for a purpose of enhancing traction,or skid resistance, of the tire tread. The presence of the E-SBR itselfis considered beneficial for a purpose of enhancing processability ofthe uncured elastomer composition mixture, especially in comparison to autilization of a solution polymerization prepared SBR (S-SBR).

By emulsion polymerization prepared E-SBR, it is meant that styrene and1,3-butadiene are copolymerized as an aqueous emulsion. Such are wellknown to those skilled in such art. The bound styrene content can vary,for example, from about 5 to about 50 percent. In one aspect, the E-SBRmay also contain acrylonitrile to form a terpolymer rubber, as E-SBAR,in amounts, for example, of about 2 to about 30 weight percent boundacrylonitrile in the terpolymer.

Emulsion polymerization prepared styrene/butadiene/acrylonitrilecopolymer rubbers containing about 2 to about 40 weight percent boundacrylonitrile in the copolymer are also contemplated as diene basedrubbers for use in this invention.

The solution polymerization prepared SBR (S-SBR) typically has a boundstyrene content in a range of about 5 to about 50, preferably about 9 toabout 36, percent. The S-SBR can be conveniently prepared, for example,by organo lithium catalyzation in the presence of an organic hydrocarbonsolvent.

A purpose of using S-SBR is for improved tire rolling resistance as aresult of lower hysteresis when it is used in a tire tread composition.

The 3,4-polyisoprene rubber (3,4-PI) is considered beneficial for apurpose of enhancing the tire's traction when it is used in a tire treadcomposition. The 3,4-PI and use thereof is more fully described in U.S.Pat. No. 5,087,668 which is incorporated herein by reference. The Tgrefers to the glass transition temperature which can conveniently bedetermined by a differential scanning calorimeter at a heating rate of10° C. per minute.

The cis 1,4-polybutadiene rubber (BR) is considered to be beneficial fora purpose of enhancing the tire tread's wear, or treadwear. Such BR canbe prepared, for example, by organic solution polymerization of1,3-butadiene. The BR may be conveniently characterized, for example, byhaving at least a 90 percent cis 1,4-content.

The cis 1,4-polyisoprene and cis 1,4-polyisoprene natural rubber arewell known to those having skill in the rubber art.

The term "phr" as used herein, and according to conventional practice,refers to "parts by weight of a respective material per 100 parts byweight of rubber, or elastomer."

The asymmetrical siloxy compounds of the present invention are of theformula ##STR10## wherein R¹, R² and R³ are independently selected fromthe group consisting of alkoxy radicals having from 1 to 8 carbon atoms;R⁴ is selected from the group consisting of alkylene groups having from1 to 15 carbon atoms and arylene and alkyl-substituted arylene groupshaving from 6 to 10 carbon atoms; n is an integer of from 2 to 8 and Xis selected from the group consisting of ##STR11## and R⁵ is selectedfrom the group consisting of alkyl groups having from 1 to 15 carbonatoms, aryl and alkyl substituted aryl groups having 6 to 20 carbonatoms. Preferably, each R¹, R² and R³ are alkoxy radicals having from 1to 3 carbon atoms, R⁴ is an alkylene group having from 1 to 3 carbonatoms, R⁵ is an alkyl group having 1 to 3 carbon atoms and X is of theFormula II, IV and VII. The asymmetrical siloxy compounds may comprise ahigh purity product or mixture of products conforming to the aboveformula.

The compounds of Formula I may be prepared according to the reactionscheme listed below. ##STR12## in the presence of Na₂ S₂ at 80 to 100°C. for 8 to 20 minutes to yield ##STR13## where Hal may be Cl, Br, etc.In those instances where the desired products contain S₄ -S₈, thereaction is conducted in the presence of Na₂ S_(x) where x is 4 to 8,depending on the desired product.

The compounds of Formula I may also be prepared according to thereaction scheme listed below ##STR14## in the presence of Na₂ S₂ toyield ##STR15##

Additional compounds of Formula I may be prepared according to thereaction scheme listed below ##STR16## in the presence of Na₂ S₂ toyield ##STR17##

Other products may be prepared by the following reaction scheme:##STR18## at 80-100° C. for 5 to 20 minutes to yield ##STR19##

Additional compounds of Formula I may be prepared according to thereaction scheme listed below ##STR20## in the presence of Na₂ S₂ toyield ##STR21##

The above reactions are generally conducted in the presence of asuitable solvent. The primary criteria is to use a solvent which doesnot react with the starting materials or end product. Representativeorganic solvents include chloroform, dichloromethane, carbontetrachloride, hexane, heptane, cyclohexane, xylene, benzene, toluene,aliphatic and cycloaliphatic alcohols. Preferably, water is avoided toprevent reaction with the siloxy groups of the compounds.

The asymmetrical siloxy compounds used in the present invention may beadded to the rubber by any conventional technique such as on a mill orin a Banbury. The amount of the asymmetrical siloxy compound may varywidely depending on the type of rubber and other compounds present inthe vulcanizable composition. Generally, the amount of the siloxycompound is used in a range of from about 0.05 to about 10.0 phr with arange of 0.1 to about 5.0 phr being preferred. The siloxy compound ispreferably added in the nonproductive stage with the silica and optionalsulfur-containing organosilicon coupling agent.

For ease in handling, the asymmetrical siloxy compound may be used perse or may be deposited on suitable carriers. Examples of carriers whichmay be used in the present invention include silica, carbon black,alumina, alumina silicates, clay, kieselguhr, cellulose, silica gel andcalcium silicate.

The rubber composition should contain a sufficient amount of silica, andcarbon black, if used, to contribute a reasonably high modulus and highresistance to tear. The silica filler may be added in amounts rangingfrom 10 to 250 phr. Preferably, the silica is present in an amountranging from 15 to 80 phr. If carbon black is also present, the amountof carbon black, if used, may vary. Generally speaking, the amount ofcarbon black will vary from 0 to 80 phr. Preferably, the amount ofcarbon black will range from 0 to 40 phr. It is to be appreciated thatthe silica coupler may be used in conjunction with a carbon black,namely pre-mixed with a carbon black prior to addition to the rubbercomposition, and such carbon black is to be included in the aforesaidamount of carbon black for the rubber composition formulation.

The commonly employed siliceous pigments used in rubber compoundingapplications can be used as the silica in this invention, includingpyrogenic and precipitated siliceous pigments (silica) andaluminosilicates, although precipitate silicas are preferred. Thesiliceous pigments preferably employed in this invention areprecipitated silicas such as, for example, those obtained by theacidification of a soluble silicate, e.g., sodium silicate.

Such silicas might be characterized, for example, by having a BETsurface area, as measured using nitrogen gas, preferably in the range ofabout 40 to about 600, and more usually in a range of about 50 to about300 square meters per gram. The BET method of measuring surface area isdescribed in the Journal of the American Chemical Society, Volume 60,page 304 (1930).

The silica may also be typically characterized by having adibutylphthalate (DBP) absorption value in a range of about 100 to about400, and more usually about 150 to about 300.

Further, the silica, as well as the aforesaid alumina andaluminosilicate may be expected to have a CTAB surface area in a rangeof about 100 to about 220. The CTAB surface area is the external surfacearea as evaluated by cetyl trimethylammonium bromide with a pH of 9. Themethod is described in ASTM D 3849 for set up and evaluation. The CTABsurface area is a well known means for characterization of silica.

Mercury surface area/porosity is the specific surface area determined byMercury porosimetry. For such technique, mercury is penetrated into thepores of the sample after a thermal treatment to remove volatiles.Set-up conditions may be suitably described as using a 100 mg sample;removing volatiles during 2 hours at 105° C. and ambient atmosphericpressure; ambient to 2000 bars pressure measuring range. Such evaluationmay be performed according to the method described in Winslow, Shapiroin ASTM bulletin, p.39 (1959) or according to DIN 66133. For such anevaluation, a CARLO-ERBA Porosimeter 2000 might be used.

The average mercury porosity specific surface area for the silica shouldbe in a range of about 100 to 300 m² /g.

A suitable pore-size distribution for the silica, alumina andaluminosilicate according to such mercury porosity evaluation isconsidered herein to be five percent or less of its pores have adiameter of less than about 10 nm; 60 to 90 percent of its pores have adiameter of about 10 to about 100 nm; 10 to 30 percent of its pores havea diameter of about 100 to about 1000 nm; and 5 to 20 percent of itspores have a diameter of greater than about 1000 nm.

The silica might be expected to have an average ultimate particle size,for example, in the range of 0.01 to 0.05 micron as determined by theelectron microscope, although the silica particles may be even smaller,or possibly larger, in size.

Various commercially available silicas may be considered for use in thisinvention such as, only for example herein, and without limitation,silicas commercially available from PPG Industries under the Hi-Siltrademark with designations 210, 243, etc; silicas available fromRhone-Poulenc, with, for example, designations of Z1165MP and Z165GR andsilicas available from Degussa AG with, for example, designations VN2,VN3, BV3380GR, etc, and silicas available from Huber, for example HuberSil 8745.

The asymmetrical siloxy compounds of Formula I may function as a silicacoupling agent. They may be used alone and/or in combination withadditional sulfur containing organosilicon compounds. Examples ofsuitable sulfur containing organosilicon compounds are of the formula:

    Z-Alk-S.sub.n -Alk-Z                                       II

in which Z is selected from the group consisting of ##STR22## where R⁶is an alkyl group of 1 to 4 carbon atoms, cyclohexyl or phenyl;

R⁷ is alkoxy of 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8 carbonatoms;

Alk is a divalent hydrocarbon of 1 to 18 carbon atoms and n is aninteger of 2 to 8.

Specific examples of sulfur containing organosilicon compounds ofFormula II which may be used in accordance with the present inventioninclude: 3,3'-bis(trimethoxysilylpropyl) disulfide,3,3'-bis(triethoxysilylpropyl) tetrasulfide,3,3'-bis(triethoxysilylpropyl) octasulfide,3,3'-bis(trimethoxysilylpropyl) tetrasulfide,2,2'-bis(triethoxysilylethyl) tetrasulfide,3,3'-bis(trimethoxysilylpropyl) trisulfide,3,3'-bis(triethoxysilylpropyl) trisulfide,3,3'-bis(tributoxysilylpropyl) disulfide,3,3'-bis(trimethoxysilylpropyl) hexasulfide,3,3'-bis(trimethoxysilylpropyl) octasulfide,3,3'-bis(trioctoxysilylpropyl) tetrasulfide,3,3'-bis(trihexoxysilylpropyl) disulfide,3,3'-bis(tri-2"-ethylhexoxysilylpropyl) trisulfide,3,3'-bis(triisooctoxysilylpropyl) tetrasulfide,3,3'-bis(tri-t-butoxysilylpropyl) disulfide, 2,2'-bis(methoxy diethoxysilyl ethyl) tetrasulfide, 2,2'-bis(tripropoxysilylethyl) pentasulfide,3,3'-bis(tricyclonexoxysilylpropyl) tetrasulfide,3,3'-bis(tricyclopentoxysilylpropyl) trisulfide,2,2'-bis(tri-2"-methylcyclohexoxysilylethyl) tetrasulfide,bis(trimethoxysilylmethyl) tetrasulfide, 3-methoxy ethoxy propoxysilyl3'-diethoxybutoxy-silylpropyltetrasulfide, 2,2'-bis(dimethylmethoxysilylethyl) disulfide, 2,2'-bis(dimethyl sec.butoxysilylethyl)trisulfide, 3,3'-bis(methyl butylethoxysilylpropyl) tetrasulfide,3,3'-bis(di t-butylmethoxysilylpropyl) tetrasulfide, 2,2'-bis(phenylmethyl methoxysilylethyl) trisulfide, 3,3'-bis(diphenylisopropoxysilylpropyl) tetrasulfide, 3,3'-bis(diphenylcyclohexoxysilylpropyl) disulfide, 3,3'-bis(dimethylethylmercaptosilylpropyl) tetrasulfide, 2,2'-bis(methyldimethoxysilylethyl) trisulfide, 2,2'-bis(methylethoxypropoxysilylethyl) tetrasulfide, 3,3'-bis(diethylmethoxysilylpropyl) tetrasulfide, 3,3'-bis(ethyl di-sec.butoxysilylpropyl) disulfide, 3,3'-bis(propyl diethoxysilylpropyl)disulfide, 3,3'-bis(butyl dimethoxysilylpropyl) trisulfide,3,3'-bis(phenyl dimethoxysilylpropyl) tetrasulfide, 3-phenylethoxybutoxysilyl 3'-trimethoxysilylpropyl tetrasulfide,4,4'-bis(trimethoxysilylbutyl) tetrasulfide,6,6'-bis(triethoxysilylhexyl) tetrasulfide,12,12'-bis(triisopropoxysilyl dodecyl) disulfide,18,18'-bis(trimethoxysilyloctadecyl) tetrasulfide,18,18'-bis(tripropoxysilyloctadecenyl) tetrasulfide,4,41-bis(trimethoxysilyl-buten-2-yl) tetrasulfide,4,4'-bis(trimethoxysilylcyclohexylene) tetrasulfide,5,5'-bis(dimethoxymethylsilylpentyl) trisulfide,3,3'-bis(trimethoxysilyl-2-methylpropyl) tetrasulfide,3,3'-bis(dimethoxyphenylsilyl-2-methylpropyl) disulfide.

The preferred sulfur containing organosilicon compounds of Formula IIare the 3,3'-bis(trimethoxy or triethoxy silylpropyl) sulfides. The mostpreferred compounds are 3,3'-bis(triethoxysilylpropyl) tetrasulfide and3,3'-bis(triethoxysilylpropyl) disulfide. Preferably Z is ##STR23##where R⁷ is an alkoxy of 2 to 4 carbon atoms, with 2 carbon atoms beingparticularly preferred; Alk is a divalent hydrocarbon of 2 to 4 carbonatoms with 3 carbon atoms being particularly preferred; and n is aninteger of from 2 to 4.

The amount of the above sulfur containing organosilicon compound ofFormula II in a rubber composition will vary depending on the level ofsilica that is used. Generally speaking, the amount of the compound ofFormula II will range from 0.00 to 1.0 parts by weight per part byweight of the silica. Preferably, the amount will range from 0.00 to 0.4parts by weight per part by weight of the silica.

In accordance with one aspect of this invention, a rubber composition isprepared by a process which comprises the sequential steps of:

(A) thermomechanically mixing in at least one preparatory mixing step toa temperature of about 140° C. to about 190° C., for a total mixing timeof about 2 to about 20 minutes (i) 100 parts by weight of at least oneelastomer containing olefinic unsaturation selected from conjugateddiene homopolymers and copolymers and copolymers of at least oneconjugated diene and aromatic vinyl compound; (ii) about 15 to about 100phr of particulate filler selected from the group consisting ofprecipitated silica, alumina, aluminosilicate, carbon black and mixturesthereof; (iii) about 0.05 to about 20 parts by weight per part by weightof said particulate filler of at least one asymmetrical siloxy compoundof the Formula I; and (iv) at least one sulfur donor having a propertyof releasing at least a portion of sulfur at a temperature in a range ofabout 140° C. to about 190° C. and selected from the group consisting ofelemental sulfur, an amine disulfide, polymeric polysulfide and sulfurolefin adducts; provided, however, that the total of said free sulfurfrom said sulfur donor addition is in a range of about 0.05 to about 2phr; and

(B) subsequently blending therewith, in a final thermomechanical mixingstep at a temperature to about 100° C. to about 130° C. for a time ofabout 1 to about 3 minutes, about 0.4 to about 3 phr of elemental sulfurprovided, however, that the total free sulfur available from said sulfurdonor addition introduced in said preparatory mixing steps and elementalsulfur added in said final mixing step is in a range of about 0.45 toabout 5 phr.

It is readily understood by those having skill in the art that therubber composition would be compounded by methods generally known in therubber compounding art, such as mixing the various sulfur-vulcanizableconstituent rubbers with various commonly used additive materials suchas, for example, sulfur donors, curing aids, such as activators andretarders and processing additives, such as oils, resins includingtackifying resins and plasticizers, fillers, pigments, fatty acid, zincoxide, waxes, antioxidants and antiozonants and peptizing agents. Asknown to those skilled in the art, depending on the intended use of thesulfur vulcanizable and sulfur vulcanized material (rubbers), theadditives mentioned above are selected and commonly used in conventionalamounts. Typical amounts of reinforcing type carbon blacks(s), for thisinvention, if used, are herein set forth. Representative examples ofsulfur donors include elemental sulfur (free sulfur), an aminedisulfide, polymeric polysulfide and sulfur olefin adducts. Preferably,the sulfur vulcanizing agent is elemental sulfur. The sulfur vulcanizingagent may be used in an amount ranging from 0.5 to 8 phr, with a rangeof from 1.5 to 6 phr being preferred. Typical amounts of tackifierresins, if used, comprise about 0.5 to about 10 phr, usually about 1 toabout 5 phr. Typical amounts of processing aids comprise about 1 toabout 50 phr. Such processing aids can include, for example, aromatic,napthenic, and/or paraffinic processing oils. Typical amounts ofantioxidants comprise about 1 to about 5 phr. Representativeantioxidants may be, for example, diphenyl-p-phenylenediamine andothers, such as, for example, those disclosed in the Vanderbilt RubberHandbook (1978), pages 344-346. Typical amounts of antiozonants compriseabout 1 to 5 phr. Typical amounts of fatty acids, if used, which caninclude stearic acid comprise about 0.5 to about 3 phr. Typical amountsof zinc oxide comprise about 2 to about 5 phr. Typical amounts of waxescomprise about 1 to about 5 phr. Often microcrystalline waxes are used.Typical amounts of peptizers comprise about 0.1 to about 1 phr. Typicalpeptizers may be, for example, pentachlorothiophenol anddibenzamidodiphenyl disulfide.

In one aspect of the present invention, the sulfur vulcanizable rubbercomposition is then sulfur-cured or vulcanized.

Accelerators are used to control the time and/or temperature requiredfor vulcanization and to improve the properties of the vulcanizate. Inone embodiment, a single accelerator system may be used, i.e., primaryaccelerator. The primary accelerator(s) may be used in total amountsranging from about 0.5 to about 4, preferably about 0.8 to about 1.5,phr. In another embodiment, combinations of a primary and a secondaryaccelerator might be used with the secondary accelerator being used insmaller amounts, such as from about 0.05 to about 3 phr, in order toactivate and to improve the properties of the vulcanizate. Combinationsof these accelerators might be expected to produce a synergistic effecton the final properties and are somewhat better than those produced byuse of either accelerator alone. In addition, delayed actionaccelerators may be used which are not affected by normal processingtemperatures but produce a satisfactory cure at ordinary vulcanizationtemperatures. Vulcanization retarders might also be used. Suitable typesof accelerators that may be used in the present invention are amines,disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides,dithiocarbamates and xanthates. Preferably, the primary accelerator is asulfenamide. If a second accelerator is used, the secondary acceleratoris preferably a guanidine, dithiocarbamate or thiuram compound.

The mixing of the rubber composition can be accomplished by methodsknown to those having skill in the rubber mixing art. For example theingredients are typically mixed in at least two stages, namely at leastone non-productive stage followed by a productive mix stage. The finalcuratives including sulfur vulcanizing agents are typically mixed in thefinal stage which is conventionally called the "productive" mix stage inwhich the mixing typically occurs at a temperature, or ultimatetemperature, lower than the mix temperature(s) than the precedingnon-productive mix stage(s). The rubber, silica, compound of Formula Iand carbon black, if used, are mixed in one or more non-productive mixstages. The terms "non-productive" and "productive" mix stages are wellknown to those having skill in the rubber mixing art. The rubbercomposition containing the compound of Formula I, rubber and generallyat least part of the silica should, as well as the sulfur-containingorganosilicon compound of Formula II, if used, be subjected to athermomechanical mixing step. The thermomechanical mixing step generallycomprises a mechanical working in a mixer or extruder for a period oftime suitable in order to produce a rubber temperature between 140° C.and 190° C. The appropriate duration of the thermomechanical workingvaries as a function of the operating conditions and the volume andnature of the components. For example, the thermomechanical working maybe from 1 to 20 minutes.

In the embodiment where at least one sulfur donor having a property ofreleasing at least the portion of sulfur is used at a temperature in arange of about 140° C. to about 190° C. during the preparatory step, theamount of sulfur donor introduced into the preparatory mixing is,generally, in a range of about 0.05 to about 2 phr. Preferably, theamount is from about 0.2 to about 1 phr. Such sulfur donor may be, forexample, in a form of elemental sulfur (S₈), or an amine disulfide,polymeric polysulfide, sulfur olefin adducts and mixtures thereof.Preferably, the sulfur donor is elemental sulfur.

The amount of free sulfur source addition to the mixture can becontrolled or manipulated as a matter of choice relatively independentlyfrom the addition of the asymmetrical siloxy compound. Thus, forexample, the independent addition of sulfur donor may be manipulated bythe amount of addition thereof and by sequence of addition relative toaddition of other ingredients to the rubber mixture such as, forexample, the silica reinforcement.

In such manner, then the asymmetrical siloxy compound of Formula I couldbe utilized for reaction with the silica and sulfur vulcanizableelastomer and the independent addition of the sulfur donor, particularlya free sulfur source, could be primarily relied upon for thevulcanization of the elastomer.

In one aspect of the invention, such process is provided wherein saidpreparatory mixing is conducted in at least two thermomechanical mixingsteps of which at least two of such mixing steps are to a temperature ina range of about 140° C. to about 190° C., with intermediate cooling ofthe rubber composition between at least two of said mixing steps to atemperature below about 50° C.

In further accordance with this invention, a rubber composition isprepared wherein preparatory steps (A) are composed of at least twosequential mixing steps in which said elastomer, said particulate fillerand said asymmetrical siloxy compounds are mixed in one or moresequential mixing steps and in which said sulfur donor is added in asubsequent sequential preparatory mixing step.

In additional accordance with another embodiment, a rubber compositionis prepared wherein said preparatory steps (A) are composed of at leasttwo sequential mixing steps in which about 20 to about 60 weight percentof the silica, the said asymmetrical siloxy compound of Formula I andsaid sulfur donor is added in the first mix step and the remainderthereof added in at least one subsequent preparatory mix step.

In accordance with another embodiment, when the asymmetrical siloxycompound of Formula I is in liquid form, it is optionally added to thethermomechanical preparatory mixing in a form of a particulate comprisedof (a) about 25 to about 75, preferably about 40 to about 60, weightpercent of said asymmetrical siloxy compound and, correspondingly, (b)about 75 to about 25, preferably about 60 to about 40, weight percentparticulate carbon black. One advantage of this embodiment is providingthe asymmetrical siloxy compound in a form of a particulate so as to addthe asymmetrical siloxy compound of Formula I in a form of a relativelydry, or substantially dry, powder in which the carbon black acts as acarrier for the asymmetrical siloxy compound since it is consideredherein that the asymmetrical siloxy compound may be liquid orsubstantially liquid. A contemplated benefit for the particulate is toaid in the dispersing of the asymmetrical siloxy compound in thepreparatory mixing step(s) of the process of this invention and to aidin the introduction of the asymmetrical siloxy compound into thepreparatory mixing of the rubber composition mixture.

In further accordance with the invention, the process comprises theadditional step of vulcanizing the prepared rubber composition at atemperature in a range of about 140° C. to about 190° C.

Accordingly, the invention also thereby contemplates a vulcanized rubbercomposition prepared by such process.

In additional accordance with the invention, the process comprises theadditional steps of preparing an assembly of a tire orsulfur-vulcanizable rubber with a tread comprised of the said rubbercomposition prepared according to the process of this invention andvulcanizing the assembly at a temperature in a range of about 140° C. toabout 190° C.

Accordingly, the invention also thereby contemplates a vulcanized tireprepared by such process.

Vulcanization of the rubber composition of the present invention isgenerally carried out at conventional temperatures ranging from about100° C. to 200° C. Preferably, the vulcanization is conducted attemperatures ranging from about 110° C. to 180° C. Any of the usualvulcanization processes may be used such as heating in a press or mold,heating with superheated steam or hot air or in a salt bath.

Upon vulcanization of the sulfur vulcanized composition, the rubbercomposition of this invention can be used for various purposes. Forexample, the sulfur vulcanized rubber composition may be in the form ofa tire, belt or hose. In case of a tire, it can be used for various tirecomponents. Such tires can be built, shaped, molded and cured by variousmethods which are known and will be readily apparent to those havingskill in such art. Preferably, the rubber composition is used in thetread of a tire. As can be appreciated, the tire may be a passengertire, aircraft tire, truck tire and the like. Preferably, the tire is apassenger tire. The tire may also be a radial or bias, with a radialtire being preferred.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

What is claimed is:
 1. A rubber composition comprising(a) an elastomercontaining olefinic unsaturation selected from the group consisting ofnatural rubber, neoprene, polyisoprene, butyl rubber, polybutadiene,styrene-butadiene copolymer, styrene/isoprene/butadiene rubber, methylmethacrylate-butadiene copolymer, isoprene-styrene copolymer, methylmethacrylate-isoprene copolymer, acrylonitrile-isoprene copolymer,acrylonitrile-butadiene copolymer, EPDM and mixtures thereof, (b)silica; and (c) an asymmetrical siloxy compound of the formula ##STR24##wherein R¹, R² and R³ are independently selected from the groupconsisting of alkoxy radicals having from 1 to 8 carbon atoms; R⁴ isselected from the group consisting of alkylene groups having from 1 to15 carbon atoms and arylene and alkyl-substituted arylene groups havingfrom 6 to 10 carbon atoms; n is an integer of from 2 to 8 and X isselected from the group consisting of ##STR25## and R⁵ is selected fromthe group consisting of alkyl groups having from 1 to 15 carbon atoms,aryl and alkyl substituted aryl groups having 6 to 10 carbon atoms. 2.The composition of claim 1 wherein each R¹, R² and R³ are alkoxyradicals having 1 to 3 carbon atoms, R⁴ is an alkylene group having 1 to3 carbon atoms and R⁵ is an alkyl group having 1 to 3 carbon atoms. 3.The composition of claim 1 wherein X is of the Formula II.
 4. Thecomposition of claim 1 wherein X is of the Formula IV.
 5. Thecomposition of claim 1 wherein X is of the Formula VII.
 6. Thecomposition of claim 1 wherein said asymmetrical siloxy compound ispresent in an amount ranging from 0.05 to 10.0 phr.
 7. The compositionof claim 1 wherein said silica is present in an amount ranging from 10to 250 phr.
 8. The composition of claim 1 wherein said elastomercontaining olefinic unsaturation is styrene-butadiene copolymer.
 9. Thecomposition of claim 1 wherein said composition was thermomechanicallymixed at a rubber temperature in a range of from 140° C. to 190° C. fora total mixing time of from 1 to 20 minutes.